1. Field of the Invention
The present invention relates to a magnetically levitated pump and, more specifically, to a clean pump utilizing a magnetic bearing, which is used, by way of example, in a medical instrument such as an artificial heart.
2. Description of the Background Art
[First Prior Art Example (Description of FIG. 11)]
FIG. 11 shows a magnetically levitated pump of a first prior art example having an electro-magnet 31 for magnetic bearing and a motor 13 provided on opposite sides of an impeller 23 (see FIG. 5 of Japanese Patent Laying-Open No. 2002-130177 and FIG. 16A of U.S. Pat. No. 6,626,644 B2). Referring to FIG. 11, the magnetically levitated pump of the first prior art example will be described. The magnetically levitated pump 1 of the first prior art example is formed of a motor unit 10, a pump unit 20 and a magnetic bearing unit 30. In a casing 21 of pump unit 20, a pump chamber 22 is provided. Impeller 23 rotates in this pump chamber 22. Impeller 23 has a plurality of blades, not shown.
Casing 21 is formed of a non-magnetic material, and impeller 23 is pivotally supported by a non-controlled magnetic bearing and a controlled magnetic bearing. The non-controlled magnetic bearing is formed of a rotor-side permanent magnet 14 and an impeller-side permanent magnet 24, while the controlled magnetic bearing is formed of an electro-magnet 31 for magnetic bearing and a soft magnetic member 27 opposite to the electro-magnet and to a position sensor. Impeller-side permanent magnet 24 is divided along the circumferential direction of impeller 23, and adjacent magnets are magnetized to have mutually opposite polarities.
Opposite to that side of impeller 23 which bears the impeller-side permanent magnet 24, a rotor 12 is provided pivotally supported by a fixed shaft 11, outside the pump chamber 22. Rotor 12 rotates, driven by motor 13. Rotor 12 has rotor-side permanent magnets 14 same in number as the impeller-side magnets, opposite to impeller-side permanent magnets 24 on impeller 23 and generating an attracting power.
In order to counterbalance the attractive force of rotor-side permanent magnets 14 and impeller-side permanent magnets 24 in the pump chamber 22 so that impeller 23 can be held at the center of pump chamber 22, three or more electro-magnets 31 for magnetic bearing and a position sensor 47 are provided on magnetic bearing unit 30. Electro-magnet 31 for magnetic bearing has a C-shape, and position sensor 47 is a magnetic sensor.
In magnetically levitated pump 1, attractive force in the axial direction acts between rotor-side permanent magnets 14 embedded in rotor 12 and impeller-side permanent magnets 24 provided on impeller 23. Magnetic coupling utilizing the attractive force is used for driving and rotating impeller 23 and for supporting impeller 23 in radial direction.
A current is caused to flow through a coil of electro-magnet 31 for magnetic bearing to counterbalance the attractive force, so that impeller 23 is lifted. When rotor 12 is rotated by the driving force of motor 13 including a motor rotor 15 and a motor stator 16, rotor-side permanent magnets 14 and impeller-side permanent magnets 24 form a magnetic coupling, whereby impeller 23 rotates, fluid is sucked in from an inlet port 23c, and emitted from an outlet port, not shown. Impeller 23 is isolated from rotor 12 by casing 21, and is free from any contamination from electro-magnets 31 for magnetic bearing, and therefore, the fluid (when applied as a blood pump, blood) emitted from magnetically levitated pump 1 is kept clean.
In this pump, however, electro-magnets 31 for magnetic bearing and motor 13 are provided on opposite sides of impeller 23, and therefore, axial length (hereinafter referred to as pump length L1) of the outer housing containing motor unit 10, pump unit 20 and magnetic bearing unit 30 becomes undesirably long. Japanese Patent Laying-Open No. 2002-130177 and U.S. Pat. No. 6,626,644 B2 also proposes a structure that addresses this problem. A second prior art example solving this problem will be described in the following.
[Second Prior Art Example (Description of FIG. 12)]
FIG. 12 shows the magnetically levitated pump of the second prior art example, in which motor 13 and electro-magnets 31 for magnetic bearing are arranged in a space on the same side (see FIG. 3 of Japanese Patent Laying-Open No. 2002-130177 and FIG. 3 of U.S. Pat. No. 6,626,644 B2) Referring to FIG. 12, the magnetically levitated pump of the second prior art example will be described. Portions having the same functions as FIG. 11 are denoted by the same reference characters, and description thereof will not be repeated.
Different from the structure shown in FIG. 11, the magnetically levitated pump shown in FIG. 12 has motor 13 and electro-magnets 31 for magnetic bearing arranged in a space on the same side. Because of this structure, the axial length of the pump (hereinafter referred to as pump length L2) consisting of an actuator unit 40, pump unit 20 and casing unit 50 is made much shorter than pump length L1 of the first prior art example shown in FIG. 11.
The magnetically levitated pump shown in FIG. 12 includes an actuator unit 40, pump unit 20 and casing unit 50. Pump chamber 22 is provided in casing 21 of pump unit 20, and impeller 23 rotates in pump chamber 22.
Casing 21 is formed of plastic, ceramic, metal or the like. Of casing 21, an electro-magnets/impeller dividing wall 35 between actuator unit 40 and impeller 23, and a position sensor/impeller dividing wall 36 between position sensor 47 and impeller 23 cannot be formed of a magnetic material. Therefore, electro-magnets/impeller dividing wall 35 and position sensor/impeller dividing wall 36 are formed of a non-magnetic material.
Impeller 23 is supported by a non-controlled magnetic bearing and a controlled magnetic bearing. The non-controlled magnetic bearing is formed of an impeller-side permanent magnet 24 and rotor-side permanent magnets 14. Controlled magnetic bearing is formed of a soft magnetic member 26 opposite to the electro-magnets for magnetic bearing of impeller 23 and electro-magnets 31 for magnetic bearing.
In rotor-side non-magnetic material 25, impeller-side permanent magnet 24 and soft magnetic member 26 opposite to the electro-magnets for magnetic bearing are embedded. Impeller-side permanent magnet 24 is divided along the circumferential direction of impeller 23, and adjacent magnets are magnetized to have mutually opposite polarities.
Opposite to that side of impeller 23 which bears the impeller-side permanent magnet 24, a rotor 12 is provided pivotally supported by a fixed shaft 11, outside the pump chamber 22. Rotor 12 rotates, driven by motor 13. Rotor 12 has rotor-side permanent magnets 14 same in number as the impeller-side magnets, opposite to impeller-side permanent magnets 24 on impeller 23 and generating an attracting power.
Opposite to soft magnetic member 26 opposite to the electro-magnets for magnetic bearing of impeller 23, electro-magnets 31 for magnetic bearing are provided.
In a non-magnetic member 46 on the side of position sensor, a ring-shaped, impeller-side ferromagnetic body 29 and a soft magnetic member 45 opposite to position sensor are embedded. Opposite to soft magnetic member 45 of impeller 23, position sensor 47 is arranged, and opposite to impeller-side ferromagnetic body 29, a ring-shaped, casing-side permanent magnet 28 is arranged. The attractive force of impeller-side ferromagnetic body 29 and ring-shaped, casing-side permanent magnet 28 also attains support of impeller 23 in the radial direction.
Impeller 23 is movable in the axial direction in pump chamber 22, and materials and shapes of casing-side permanent magnet 28 and impeller-side ferromagnetic body 29 as well as the arrangement of casing-side permanent magnet 28 are determined so that the attractive force acting between casing-side permanent magnet 28 and impeller-side ferromagnetic body 29 is always larger than the attractive force acting on impeller-side permanent magnets 24 and rotor-side permanent magnets 14 within this movable range.
Using position sensor 47 and electro-magnets 31 for magnetic bearing, the attractive force acting between impeller-side permanent magnets 24 and rotor-side permanent magnets 14 is counterbalanced by the attractive force acting between impeller-side ferromagnetic body 29 and casing-side permanent magnet 28, whereby impeller 23 can be held at the center of pump chamber 22.
Magnetically levitated pump 1 shown in FIG. 11 has a problem that axial length of electro-magnets 31 for magnetic bearing in magnetic bearing unit 30 is long, and therefore pump length L1 including motor unit 10, pump unit 20 and magnetic bearing unit 30 becomes long.
In order to solve this problem, in the example of FIG. 12, magnetic bearing unit 30 and motor 13 are arranged in a space on the same side, so that the pump length including actuator unit 40, pump unit 20 and casing unit 50, that is, the pump length L2 along the axial direction mentioned above, is made shorter than pump length L1 of the first prior art example shown in FIG. 11, and the entire pump is made compact. When the magnetically levitated pump is to be used as an implanted blood pump, however, further size reduction of the pump is desirable.